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Abstract

Background

Determining surgical treatment is difficult in blunt abdominal trauma (BAT) patients with isolated free fluid without solid organ injury (IFFWSOI) on abdominal computed

tomography (CT). We investigated the laboratory, clinical, and radiologic features of BAT patients with IFFWSOI on abdominal CT requiring surgery.

Methods

A retrospective medical record review was performed for patients treated at our government-established regional tertiary trauma center from March 2014 to August 2018. A

total of 501 patients were identified and reviewed. Patients were divided into Surgery and No Surgery groups for analysis. The Surgery group included patients who

underwent surgery during the index admission, while the No Surgery group included patients who did not undergo surgery.

Results

There were significantly more cases of severe fluid collection (61.5% vs. 11.8%; p < 0.001), car accidents (69.2% vs. 35.3%; p = 0.018), and abdominal pain (87.2% vs.

58.8%; p = 0.031) at the emergency department in the Surgery group. Regarding laboratory studies performed at the emergency department, only the me dian amylase level

was significantly higher in the No Surgery group (54.5 U/L vs. 62.5 U/L; p = 0.048). On multivariate logistic regression analysis with adjustments for age and sex, the odds

ratio (OR) for severe fluid collection on abdominal CT to predict surgery was 13.52 (p = 0.006), while the OR for abdominal pain was 7.34 (p = 0.036) and the OR for car

accident was 2.14 (p = 0.329). In addition, a multivariate logistic regression with adjustment for age, sex, delta neutrophil index, and C-reactive protein, showed the same

propensity as the other model, although statistical significance was retained only for severe fluid collection.

Conclusion

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Surgical treatment should be actively considered in the presence of a large volume of intra-abdominal free fluid, especially when concomitant with abdominal pain or after

car accidents in BAT patients without solid organ injury.

Key words

Intra-abdominal isolated free fluid; abdominal computed tomography; surgery

Introduction

Studies have recommended mandatory surgery in cases with abdominal computed tomography (CT) findings of isolated free fluid without solid organ injury (IFFWSOI) in

blunt abdominal trauma patients because it indicates the possibility of hollow viscus injuries [1,2]. However, other studies have suggested that surgery is not necessary in all

cases of IFFWSOI in blunt abdominal trauma patients[3,4]. Hollow viscus and mesenteric injuries occur in 1–5% of patients with blunt abdominal trauma[5-7]. They are

notoriously difficult to diagnose, particularly in cases of multiple distracting injuries. A missed small bowel injury, the diagnosis for which is delayed by as few as 8–12

hours, increases the morbidity and mortality rates from peritonitis and sepsis[8]. Meanwhile, unnecessary laparotomy results in significant morbidity[9]. Appropriate

decision-making about surgical treatment is very important in blunt abdominal trauma patients with IFFWSOI. Although there are many studies on the diagnosis of hollow

viscus injury, few studies to date have combined CT image, laboratory, and physical examination findings[10]. In addition, there is no ‘gold standard’ diagnostic approach to

assess patients with suspected hollow viscus injury[11]. We hypothesized that the combination of laboratory, clinical, and radiologic findings would increase the diagnostic

accuracy of surgical hollow viscus injury in blunt abdominal trauma patients with IFFWSOI on abdominal CT. This study investigated the laboratory, clinical, and radiologic

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features of blunt abdominal trauma patients with IFFWSOI on abdominal CT requiring surgery.

Methods

This retrospective study was approved by the institutional review board of our institution and was registered on Research Registry (http//:researchregistry.com). This work

has been reported in accordance with the guidelines of the STROCSS criteria[12].

A retrospective medical record review was performed of patients treated at our government-established regional tertiary trauma center (mimicking a level 1 trauma center in

the USA) between March 2014 and August 2018. A total of 13,167 patients had a diagnosis of abdominal trauma including simple abdominal wall contusion. Patients were

categorized into the Surgery and No Surgery groups. The Surgery group included patients who underwent abdominal surgery during the index admission, while the No

Surgery group included patients who did not undergo any abdominal surgery during the index admission. At our institution, the practice is to perform laparotomy for patients

with IFFWSOI on abdominal CT in patients with blunt abdominal trauma, but the final decision is left to the attending surgeon. The differences between the two groups were

investigated to determine factors that predict the need for surgery with regards to laboratory, clinical, and radiologic features. Inclusion criteria were as follows: blunt

abdominal trauma patients; hemodynamically stable (e.g. mean arterial pressure >60 mmHg) patients; and patients who were subjected to abdominal CT within 30 hours from

the index accident time. We excluded patients with an Abbreviated Injury Scale code related to a retroperitoneal hematoma, genitourinary tract injury except bladder injury,

solid organ injury, and penetrating injury. We prepared a patient list to review CT images on the basis of the aforementioned inclusion and exclusion criteria. The abdominal

CT images of these patients were reviewed independently by two trauma surgeons (one with 7 and the other with 5 years’ experience working at our trauma center) on

standard PACS workstations (Centricity™; GE Healthcare, USA). The surgeons were given no clinical information except that the patients were selected based on the

aforementioned inclusion and exclusion criteria. If there was a discrepancy between the results of either reviewer, the case was excluded. Patients with findings of active

contrast leakage or intraperitoneal free gas on abdominal CT images, which is usually considered an absolute surgical indication, were excluded as we wanted to investigate

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only the factors predicting the need for surgery in blunt abdominal trauma patients with IFFWSOI on abdominal CT without an absolute surgical indication.

Abdominal regions were separated into the pelvis, right paracolic gutter, left paracolic gutter, perisplenic area, perihepatic area, and the area between bowel loops. The

number of abdominal regions in which fluid had collected was considered an indirect indicator of the extent of IFFWSOI[13-15]. Severe fluid collection was defined as the

presence of fluid collection in more than three of the aforementioned abdominal regions on CT. The largest dimension of intraperitoneal free fluid collection perpendicular to

the axial plane was recorded in each case. The mean attenuation (in Hounsfield units [HU]) of the largest intraperitoneal free fluid collection in the axial plane of enhanced

abdominal CT images was recorded using an oval region of interest[4]. As our trauma center is a regional tertiary referral center (58.4% of patients in this study underwent

their first abdominal CT at another hospital), the CT protocols used and specifications were diverse.

The patients’ electronic medical records were reviewed for parameters including premedical history, injury mechanism, vital signs, presence of abdominal pain, presence of

abdominal tenderness, seatbelt sign, and time interval between the accident and CT and that between the accident and laparotomy. In addition, clinical outcomes were

compared between the Surgery group and the No Surgery group to show that there were no differences in clinical outcomes, as we hypothesized that not all IFFWSOI cases

mandate laparotomy.

Statistical analysis

Normality was assessed using the Shapiro-Wilk test. Categorical variables are presented as frequencies and percentages. Continuous variables are presented as means and

standard deviations (SD) or as medians and interquartile ranges (IRQ). The chi-square test or Fisher’s exact test was performed to compare the categorical variables. The

Mann-Whitney U test was conducted to compare continuous variables. Cohen’s kappa was used to determine the inter-rater reliability between Rater 1 and Rater 2 in terms of

the abdominal CT image findings. Variables with p-values <0.05 in the univariate analysis were included in the multivariate logistic regression analysis to identify predictors

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of surgery. To evaluate the accuracy of predictive factors of surgery, the area under the curve (AUC) was determined using receiver operating characteristic (ROC) curves.

The optimal cut-off point was determined using the maximum Youden index. R Package ggplot2 was used to create the boxplot. P-values <0.05 were considered statistically

significant. The analysis was performed using SPSS version 23 (IBM, Armonk, NY, USA), R version 3.5.2 (The R Foundation for Statistical Computing, Vienna, Austria),

and MedCalc Statistical Software version 17.5.3 (MedCalc Software, Ostend, Belgium).

Results

Characteristics of study participants

Abdominal CT images were reviewed for 501 patients. Of these, 375 patients were excluded, as there was no fluid collection on abdominal CT noted by each reviewer.

Forty-nine patients were excluded owing to disagreement between the two reviewers regarding these cases. Twenty-one patients were excluded due to findings of active

contrast leakage on abdominal CT presenting an absolute indication for surgery. Thus, total of 56 patients were analyzed in this study. The patient baseline clinical

characteristics stratified by group are listed in Table 1. The median age was 54 years, and men constituted 75.0% of the study group. As hemodynamic instability was a

contraindication for abdominal CT, the mean arterial pressure of all patients was 60 mmHg or more. There were 39 patients in the Surgery group and 17 in the No Surgery

group (69.6% vs. 30.4%, respectively). The median largest dimension of intraperitoneal free fluid collection perpendicular to the axial plane was 90.0 cm and 70.0 cm (p =

0.154) and the mean HU was 34.3 and 32.7 (p = 0.726) in the Surgery and No Surgery groups, respectively. There were significantly more cases of severe fluid collection

(61.5% vs. 11.8%; p < 0.001), car accidents (69.2% vs. 35.3%; p = 0.018), and abdominal pain (87.2% vs. 58.8%; p = 0.031) at the emergency department in the Surgery

group. Chronic liver disease occurred more frequently in the No Surgery group (0.0% vs. 11.8%; p = 0.031). Meanwhile, there were no statistically significant differences in

other underlying diseases and past abdominal surgery. There were no statistically significant differences in the findings of laboratory studies performed at the emergency

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department except in the amylase level. The median amylase level was significantly higher in the No Surgery group (54.5 [42.0-69.5] vs. 62.5 [55.3-89.5]; p = 0.048).

A total of 47 surgical procedures were performed in 39 patients of the Surgery group (Supplement table 1). Regarding operative findings, there were 19 full-layer intestinal

injuries including 1 case of terminal ileum segmental infarction, 7 of active bleeding in the mesentery or omentum, 6 of full-layer mesenteric lacerations, 3 of intraperitoneal

bladder rupture, 1 of gall bladder rupture, 1 of abdominal aortic dissection with occlusion, 1 of teratoma rupture with dirty material soiling the peritoneal cavity, and 1 of

active perineal bleeding. Because all Surgery group patients had more than one of the aforementioned operative findings, all surgeries were considered to be therapeutic.

There were no significant differences in clinical outcomes between the Surgery and No Surgery groups (Supplement table 2). In the subgroup analysis, the initial treatment

plan was non-operative management in 22 patients; of these, the non-operative plan failed in 5, with intestinal resection and anastomosis being required in 2 patients and

intestinal primary repair, cholecystectomy, and bladder repair in 1 each. Abdominal complications occurred more frequently in the failed non-operative management group

than in the Surgery group patients (40.0% vs. 29.4%; p = 0.634). The failed non-operative management group more frequently demonstrated severe fluid collection than the

successful non-operative management group (e.g. No Surgery group) (60.0% vs. 11.8%; p = 0.55), but the difference was not statistically significant.

Cohen's kappa of inter-rater evaluations of CT images

Cohen’s kappa values were derived to confirm the consistency between the CT image readings of the two observers in regard to intra-abdominal free fluid collection on

abdominal CT. The kappa value for fluid collection was 0.70, showing substantial agreement of over 0.60 (Supplement table 3).

Surgery prediction model

The median number of abdominal regions containing fluid collection differed between the Surgery and No Surgery group boxplots. On a jitter plot, most of the No Surgery

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group patients were distributed below 3, and the Surgery group patients were distributed uniformly in the whole plot (Figure 1). Therefore, the cut-off for the number of

abdominal regions with fluid collection predictive of surgery was set to 3 based on the ROC curve (sensitivity, 61.5%; specificity, 88.2%). On univariate logistic regression

analysis, the odds ratio (OR) for severe fluid collection on abdominal CT to predict surgery was 12.00 (p = 0.002), while the OR for abdominal pain was 4.76 (p = 0.023), and

the OR for car accident was 4.13 (p = 0.021). Severe fluid collection had the highest OR among the variables with p-value <0.05 in the univariate analysis. Predictors of

surgery obtained via univariate logistic regression analyses are listed in Supplement table 4. Furthermore, we analyzed Model 1 using multivariate logistic regression with

adjustment for age and sex. The OR for severe fluid collection on abdominal CT to predict surgery was 13.52 (p = 0.006), while the OR for abdominal pain was 7.34 (p =

0.036) and the OR for a car accident was 2.14 (p = 0.329) (AUC, 0.866; 95% CI, 0.748–0.942). Model 2 using multivariate logistic regression included adjustment for age,

sex, delta neutrophil index, and C-reactive protein. Except for severe fluid collection, the differences in other variables were not statistically significant; however, Model 2

showed the same propensity as the other model (AUC, 0.863; 95% CI, 0.743–0.942). The p-value for the difference between the AUC of the two models was 0.790, which

was not statistically significant (Table 2, Figure 2).

Discussion

Excluding solid organ injuries in blunt abdominal trauma, the usual causes of intra-abdominal fluid collection on abdominal CT are a perforated bowel and a mesentery

injury. The present study showed similar results. Among 47 surgeries in 56 patients in this study, 19 (41.3%) surgeries were intestinal repairs and 16 (34.8%) were mesentery

repairs. The clinical significance of the IFFWSOI is related to bowel or mesentery injury requiring surgical treatment in blunt abdominal trauma patients. However, it is not a

pathognomonic sign of surgical mesentery or bowel injury. Bennett et al. reported in a recent literature review that intra-abdominal fluid collection findings on abdominal CT

were highly sensitive (90–100%) for surgical mesenteric and bowel injuries; however, the specificity was low at only 15–26% in blunt abdominal trauma patients [16]. This

high sensitivity and low specificity of intra-abdominal fluid collection on abdominal CT for the diagnosis of surgical bowel and mesentery injury resulted in a high non-

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therapeutic laparotomy rate when the intra-abdominal fluid collection on abdominal CT is the sole laparotomy indication. Although operating in all cases of intra-abdominal

fluid collection on abdominal CT in blunt trauma patients without a solid organ injury is helpful to prevent adverse outcomes associated with missed injuries, the morbidity

and costs of negative laparotomy are considerable[9,17]. For this reason, studies have identified the definitive surgical indications for the patients with intra-abdominal fluid

collection on abdominal CT in blunt abdominal trauma patients without solid organ injuries. McNutt et al. developed a new CT grading scale for mesentery injury in blunt

bowel injury. The grading system consists of 5 steps. In the grading system, there is no intra-abdominal fluid collection on abdominal CT in cases with grades 1, 2, and 3,

which include only mesentery hematoma. Grade 4 includes mesenteric contusion or hematoma (any size) with associated bowel wall thickening or adjacent inter-loop fluid

collection, while grade 5 is active vascular or oral contrast extravasation, bowel transaction, or pneumoperitoneum. Cases with grade 5 were excluded from the analysis. In

the McNutt’s study, the presence of CT grade 4 injury alone increased the risk of surgical bowel injury by nine times. The McNutt’s study showed the clinical significance of

intra-abdominal fluid collection on abdominal CT for detecting surgical bowel injury as a surgical indication. They developed an unweighted bowel injury prediction score

(BIPS) with 1 point given for a grade 4 CT scan, reported abdominal tenderness at the emergency department, and a white blood cell count 17,000/µL or higher on admission.

Patients with a mesenteric or bowel abnormality on CT scan with a BIPS of ≥2 were 19 times more likely to have a surgical bowel injury[18]. Gonser-Hafertepen et al.

reported that abdominal tenderness and moderate to large intra-abdominal fluid collection on abdominal CT showed a positive predictive value of 62% and negative

predictive value of 97% for initial workup characteristics when determining operative intervention[13]. Our study results were somewhat in agreement with these previous

results. The proportion of cases with severe fluid collection was 61.5% in the Surgery group and 11.8% in the No Surgery group; the difference was statistically significant.

On univariate logistic regression analysis, the OR for severe fluid collection on abdominal CT to predict the need for surgery was 12.00 ( p = 0.002). In addition, in Model 2,

multivariate logistic regression with adjustment for age, sex, delta neutrophil treatment, and C-reactive protein showed an OR of 13.88. However, abdominal pain and

abdominal tenderness at the emergency department failed to show statistically significant differences for predicting surgery in the multivariate logistic regression analysis.

There are many confounders associated with abdominal pain and tenderness, especially in trauma patients in the emergency department. Detecting abdominal pain and

tenderness in patients with head and abdominal trauma is difficult[19-21]. Dennis et al. reported that the incidence of an abdominal wall injury identified on CT was 9% in

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blunt abdominal trauma patients. Abdominal wall injury was divided into five stages in their study: grade 1, subcutaneous tissue contusion; grade 2, abdominal wall

hematoma; grade 3, single abdominal wall muscle disruption; grade 4, complete abdominal wall disruption with herniation of abdominal contents; grade 5, complete

abdominal wall disruption with evisceration. Grade 1 and 2 injuries, which do not mandate surgery, occurred in 81.4% of patients [22]. Abdominal wall injury does not equal

an intraperitoneal hollow viscus organ injury, which requires mandatory surgery, but since it can cause abdominal pain and tenderness, it can confound decision making.

Bader et al. suggested the limited value of physical tests and laboratory parameters for diagnosing abdominal sepsis[23]. The findings of peritonitis and a seatbelt sign had

100% specificity, but the sensitivities were 37.5% and 25%, respectively, in blunt abdominal trauma patients[24]. Some studies suggested that abdominal pain and tenderness

showed low sensitivities for detecting intra-abdominal injuries that require mandatory surgery after blunt abdominal trauma in selected clinical settings [25-27]. We originally

assumed that abdominal pain and tenderness, which were traditionally important factors for predicting surgical mesentery and bowel injuries, would complement the intra-

abdominal fluid collection on abdominal CT for surgical decision-making processes. The role of abdominal pain and tenderness in detecting surgical mesentery and

abdominal injuries was disappointing in the present study. This result may be partially attributed to the study’s relatively small sample size.

As it is difficult to evaluate the exact volume of intra-abdominal fluid collection on abdominal CT images, some studies have measured the intra-abdominal fluid collection

on abdominal CT images using an indirect indicator[4,13-15,28]. The mean largest dimension of intraperitoneal free fluid collection perpendicular to the axial plane was used

as an indirect indicator in the present study. It was larger in the Surgery group than in the No Surgery group, although the difference was not significant. The failure to show

statistical differences may be due to the small number of subjects. Meanwhile, there may be other factors that affect the accuracy of the results. When fluid is collected in the

perihepatic or perisplenic space, their dimensions may be elongated due to being compressed by the liver or spleen.

Regarding the HU, there were no statistically significant differences between the Surgery and No Surgery group. The attenuation values of fluid, including bile, urine and

intestinal contents range from 0 to 15 HU. Blood usually has a higher measured attenuation than other aforementioned body fluids; however, its attenuation may vary in

various clinical settings by age, hemorrhage location, serum hematocrit level, and interval between the initiation of bleeding and CT scan[29]. The absolute indications of

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laparotomy in blunt abdominal trauma patients with intra-abdominal fluid collection on abdominal CT are hollow viscus perforation or infarction. Intraperitoneal bleeding

itself is not an indication of laparotomy unless it causes hemodynamic instability. It is reasonable to assume that fluid collection owing to intra-abdominal organ injury

without hollow viscus perforation (intestine, gall bladder, and bladder) may show higher HU values as blood usually has a higher measured attenuation than other body fluids.

Thus, there are more absolute surgical indications in blunt abdominal trauma patients with lower HU values at the fluid collection site. The lower the HU of fluid collection,

the more likely is the possibility of hollow viscus injury for the causes mentioned above. In the subgroup analysis, the Surgery group was categorized into the Hollow Viscus

Perforation group and the No Hollow Viscus Perforation group based on the operative records. Cases in the No Surgery group were all categorized into No Hollow Viscus

Perforation group because there were no absolute surgical indications during index admission. The No Hollow Viscus Perforation group showed a significantly higher mean

HU at the largest intraperitoneal free fluid collection in the axial plane of enhanced abdominal CT (Supplement table 5). This means that more of the intra-abdominal fluid

collection are composed of blood in the No Hollow Viscus Perforation group than the Hollow Viscus Perforation group. Although the range of HU values which indicate that

the patient can be safely observed without surgery were not determined in the present study, a high HU value of the intra-abdominal fluid collection on abdominal CT

indicates a relatively low chance of mandatory surgery in hemodynamically stable blunt abdominal trauma patients.

Some studies have reported that serum amylase levels are elevated in patients with intestinal injury[30-33]. Thus, we assumed that blood amylase level would also be

elevated in patients with intestinal damage. However, we found that the amylase level was higher in the No Surgery group than Surgery group. We assumed that the error was

caused by the small sample size. In fact, the three highest patient amylase levels were 127 U/L, 228 U/L, and 301 U/L in the No Surgery group and 104 U/L, 104 U/L, and

113 U/L in the Surgery group. This coincidence may cause an error due to the relatively small number of patients in this study.

A strength of our study is that we combined laboratory, clinical, and radiologic features and analyzed these characteristics to identify surgical indications in blunt abdominal

patients with IFFWSOI on abdominal CT images. However, there are several limitations to the present study. First, it was a retrospective study, meaning that surgical

indications were not always consistent. In principle, our institution provides surgical treatment if there is a certain volume of intra-abdominal isolated fluid collection without

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solid organ injury detectable on the abdominal CT image with the diagnostic impression of surgical hollow viscus injuries. However, there may be some differences in

surgical indications from case to case, as it is difficult to calculate the exact intra-abdominal fluid collection volumes. Second, despite the trauma field experience of the two

trauma surgeons who reviewed abdominal CT images, there is no definitive method to ensure their expertise in reviewing CT results. Third, no laparoscopic surgery case was

included in this study. There are several papers describing the feasibility and effectiveness of laparoscopic surgery in stable blunt abdominal trauma patients [34-36].

Laparoscopic surgery reduces the postoperative pain, adhesive ileus, and surgical site infections. In addition, it reduces complications of negative laparotomy in

hemodynamically stable trauma patients. As laparoscopic surgery can directly discriminate between surgical hollow viscus injury and non-surgical intra-abdominal organ

injury, the clinical outcome of our patients would likely have changed if we had performed laparoscopic surgery. During the study period, our institution did not perform

laparoscopic surgery in trauma patients because we adopted a “the faster the better” approach in the trauma field. However, we recently, after the study period, have begun to

perform laparoscopic surgery in hemodynamically stable blunt abdominal trauma patients as we have realized that the ‘old dogma’ may be disregarded considering the

accumulated literature favoring laparoscopic surgery in hemodynamically stable blunt abdominal trauma patients. Fourth, the sample size of the present study was small,

leading to insufficient statistical power. Because IFFWSOI on abdominal CT is a rare finding, a multicenter study is necessary to validate our findings.

In the present study, severe fluid collection was the most reliable predictor of surgery requirement in blunt abdominal trauma patients without solid organ injury. Meanwhile,

among variables which showed statistical significance in univariate analysis, abdominal pain at emergency department and mechanism of car accident showed limited value

in predicting the requirement for surgery. In addition, as chronic liver disease was present in only two of 56 patients, so we thought that the result occurred by chance due to

the small sample size. Thus, we excluded the variable, chronic liver disease, from multivariate analysis. Although there are many confounders associated with abdominal

pain, we think that no abdominal pain is very reliable sign to excluding the requirement for surgery in blunt abdominal patients with clear mentality. In regard to mechanism

of car accident, the analysis result may not be accurate because it was not analyzed according to the speed of car at the crash moment. However, mechanism of car accident

plays an important role in predicting the need for surgery because of the potential for high energy accident. Although mechanism of car accident showed limited value in

predicting surgery in the present study, we think it is one of the important predictor of surgery requirement for the aforementioned cause.

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In conclusion, surgical treatment should be actively considered when there is a large amount of intra-abdominal free fluid, especially in the presence of abdominal pain or

after a car accident, in blunt abdominal trauma patients without solid organ injuries.

Conflict of interest: None declared.

Acknowledgments

We would like to thank Editage (www.editage.co.kr) for English language editing

Provenance and peer review

Not commissioned, externally peer-reviewed

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viscus injury in blunt trauma patients with unexplained intraperitoneal free fluid without solid organ injury, Am. J. Surg. 213 (5) (2017) 874-880.

[25] R.C. Mackersie, A.D. Tiwary, S.R. Shackford, et al., Intra-abdominal injury following blunt trauma. Identifying the high-risk patient using objective risk factors, Arch. Surg. 124 (7) (1989) 809-813.

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[27] A.B. Peitzman, M.S. Makaroun, B.S. Slasky, et al., Prospective study of computed tomography in initial management of blunt abdominal trauma, J. Trauma 26 (7) (1986) 585-592.

[28] J. Charbit, I. Millet, O. Martinez, et al., Does the size of the hemoperitoneum help to discriminate the bleeding source and guide therapeutic decisions in blunt trauma patients with pelvic ring fracture?, J Trauma Acute Care Surg 73 (1) (2012) 117-125.

[29] M. Lubner, C. Menias, C. Rucker, et al., Blood in the belly: CT findings of hemoperitoneum, Radiographics 27 (1) (2007) 109-125.[30] C.W. Chase, D.E. Barker, W.L. Russell, et al., Serum amylase and lipase in the evaluation of acute abdominal pain, Am. Surg. 62 (12)

(1996) 1028-1033.[31] C. Wilson, C.W. Imrie, Amylase and gut infarction, Br. J. Surg. 73 (3) (1986) 219-221.[32] R.P. Singh, N. Garg, A.S. Nar, et al., Role of Amylase and Lipase Levels in Diagnosis of Blunt Trauma Abdomen, J Clin Diagn Res 10

(2) (2016) PC20-23.[33] S. Kumar, S. Sagar, A. Subramanian, et al., Evaluation of amylase and lipase levels in blunt trauma abdomen patients, J. Emerg.

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hollow viscus and mesenteric injuries, Am. J. Surg. 210 (2) (2015) 326-333.[35] H.F. Lin, Y.D. Chen, S.C. Chen, Value of diagnostic and therapeutic laparoscopy for patients with blunt abdominal trauma: A 10-year

medical center experience, PLoS One 13 (2) (2018) e0193379.[36] M. Khubutiya, P.A. Yartsev, A.A. Guliaev, et al., Laparoscopy in blunt and penetrating abdominal trauma, Surg. Laparosc. Endosc.

Percutan. Tech. 23 (6) (2013) 507-512.

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Table 1. Baseline clinical characteristics of patients in the Surgery and No Surgery groups.

Variable Total (N = 56) Surgery (n = 39) No Surgery (n = 17) P- value

Age (years) 54.0 [43.5-63.8] 54.0 [45.0-63.0] 53.0 [42.5-70.0] 0.986

Sex (male) 42 (75.0%) 29 (74.4%) 13 (76.5%) 1.000

Diabetes mellitus 6 (10.7%) 3 (7.7%) 3 (17.6%) 0.354

Hypertension 11 (19.6%) 5 (12.8%) 6 (35.3%) 0.071

Chronic liver disease 2 (3.6%) 0 (0.0%) 2 (11.8%) 0.031

Ischemic heart disease 2 (3.6%) 1 (2.6%) 1 (5.9%) 0.519

COPD 1 (1.8%) 0 (0.0%) 1 (5.9%) 0.304

Car accident 33 (58.9%) 27 (69.2%) 6 (35.3%) 0.018

Past abdominal surgery 6 (10.7%) 3 (7.7%) 3 (17.6%) 0.354

Abdominal pain at ED 44 (78.6%) 34 (87.2%) 10 (58.8%) 0.031

Abdominal tenderness at ED 30 (53.6%) 23 (59.0%) 7 (41.2%) 0.219

Seatbelt sign 7 (12.5%) 6 (15.4%) 1 (5.9%) 0.421

Severe fluid collection 26 (46.4%) 24 (61.5%) 2 (11.8%) <0.001

Largest dimension (mm) 84.5 [55.0-132.5] 90.0 [55.0-140.0] 70.0 [50.0-105.0] 0.154

HU 33.8 ± 16.1 34.3 ± 16.4 32.7 ± 15.7 0.726

Accident to CT time (min) 175.5 [91.5-275.3] 174.0 [91.0-270.0] 184.0 [98.5-333.0] 0.656

Accident to laparotomy time (min) 320.0 [235.0-435.0] 320.0 [235.0-435.0] N/A N/A

Body temperature at ED 36.5 [36.0-36.9] 36.5 [36.0-36.9] 36.5 [35.7-36.8] 0.474

Systolic blood pressure at ED 126.1 ± 22.8 122.9 ± 17.8 133.4 ± 30.8 0.205

Diastolic blood pressure at ED 74.6 ± 15.2 72.6 ± 14.0 79.1 ± 17.3 0.149

Respiratory rate at ED (per min) 18.0 [18.0-20.0] 18.0 [18.0-20.0] 20.0 [18.0-20.0] 0.404

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Heart rate at ED (per min) 87.0 ± 13.8 85.8 ± 12.4 89.6 ± 16.7 0.353

GCS at ED 15.0 [15.0-15.0] 15.0 [15.0-15.0] 15.0 [15.0-15.0] 0.860

Injury severity score 9.0 [5.0-14.0] 9.0 [5.0-13.0] 10.0 [5.0-15.5] 0.289

Hemoglobin at ED 13.1 ± 2.2 13.2 ± 2.2 12.7 ± 2.3 0.459

pH at ED 7.4 ± 0.1 7.4 ± 0.1 7.4 ± 0.1 0.499

Delta neutrophil index at ED 0.2 [0.0-2.3] 0.0 [0.0-2.2] 0.9 [0.0-2.3] 0.472

CRP 0.3 [0.3-0.4] 0.3 [0.3-0.4] 0.3 [0.3-0.5] 0.778

White blood cell count at ER (per dL) 14,410 [9,595-19,052] 14,440 [11,020-21,010] 12,510 [8,710-17,890] 0.417

Neutrophil (%) at ED 82.5 [73.7-88.2] 82.7 [75.0-88.5] 82.5 [72.7-88.4] 0.762

Amylase (U/L) at ED 57.0 [45.8-72.3] 54.5 [42.0-69.5] 62.5 [55.3-89.5] 0.048

Lipase (U/L) at ED 168.5 [115.0-238.3] 162.0 [103.5-240.5] 177.0 [154.0-242.0] 0.115

Lactate (mmol/L) at ED 1.8 [1.0-2.6] 1.9 [1.0-3.3] 1.8 [1.0-2.4] 0.508

COPD, chronic obstructive pulmonary disease; ED, emergency department; HU, Hounsfield unit; CT, computed tomography; GCS, Glasgow comma scale; CRP, C-reactive protein

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Table 2. Predictors of surgery requirement on univariate and multivariate logistic regression analysis

VariableUnivariate

P-valueModel 1

P-valueModel 2

P- valueOR (95% CI) OR (95% CI)* OR (95% CI)†

Severe fluid collection 12.00 (2.40-60.05) 0.002 13.52 (2.08-87.82) 0.006 13.88 (2.09-92.23) 0.006

Abdominal pain at ED 4.76 (1.24-18.31) 0.023 7.34 (1.14-47.27) 0.036 4.47 (0.59-34.14) 0.149

Mechanism of car accident 4.13 (1.24-13.76) 0.021 2.14 (0.46-9.90) 0.329 2.26 (0.46-11.19) 0.317

OR, odds ratio; CI, confidence interval; DNI, delta neutrophil index; CRP, C-reactive protein*Multivariate logistic regression analysis adjusted for age and sex. †Multivariate logistic regression analysis adjusted for age, sex, CRP, and DNI.

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Supplement table 1. Operations performed in the Surgery group

Type of procedure Number

Intestinal resection and anastomosis 14

Intestinal primary repair 4

Mesentery repair 16

End colostomy 1

Omental bleeding control 4

Tape packing 1

Bladder repair 3

Primary repair of perineum 1

Teratoma removal 1

Cholecystectomy 1

Aortoiliac bypass 1

Total 47

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Supplement table 2. Clinical outcomes of patients in the Surgery and No Surgery groups.

Variable Total (N = 56) Surgery (n = 39) No surgery (n = 17) P-value

Ileus 10 (17.9%) 9 (23.1%) 1 (5.9%) 0.253

Bowel leakage 1 (1.8%) 1 (2.6%) 0 (0.0%) 1.000

Intra-abdominal

abscess2 (3.6%) 2 (5.1%) 0 (0.0%) 1.000

Mortality 3 (5.4%) 1 (2.6%) 2 (11.8%) 0.216

Readmission 3 (5.4%) 3 (7.7%) 0 (0.0%) 0.546

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Supplement table 3. Inter-rater reliability of the screening tests used in this study

Rater 1 outcomes Rater 2 outcomes Kappa (95% CI)Yes, n (%) No, n (%) Yes, n (%) No, n (%)

Fluid collection 103 (20.6) 398 (79.4) 100 (20.0) 401 (80.0) 0.70 (0.62–0.78)

CI, confidence interval

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Supplement table 4. Predictors of surgery via univariate logistic regression analysis

Variable Odds ratio 95% CI P-value

Age (years) 1.00 0.97-1.04 0.980

Sex (male) 1.12 0.30-4.24 0.867

Diabetes mellitus 0.39 0.70-2.16 0.280

Hypertension 0.27 0.07-1.06 0.060

Chronic liver disease - - -

Ischemic heart disease 0.42 0.03-7.15 0.550

COPD - - -

Car accident 4.13 1.24-13.76 0.021

Past abdominal surgery 0.39 0.70-2.16 0.280

Abdominal pain at ED 4.76 1.24-18.31 0.023

Abdominal tenderness at ED 2.05 0.65-6.54 0.223

Seatbelt sign 2.91 0.32-26.24 0.341

Severe fluid collection 12.00 2.40-60.05 0.002

Largest dimension (mm) 1.01 1.00-1.02 0.140

HU 1.01 0.97-1.04 0.721

Accident to CT time (min) 1.00 1.00-1.00 0.839

Accident to laparotomy time (min) - - -

Body temperature at ED 1.54 0.72-3.26 0.263

Systolic blood pressure at ED 0.98 0.95-1.01 0.121

Diastolic blood pressure at ED 0.97 0.93-1.01 0.152

Respiratory rate at ED (per min) 1.00 0.77-1.29 0.861

Heart rate at ED (per min) 0.98 0.94-1.02 0.347

GCS at ED 1.17 0.92-1.48 0.198

Injury severity score 0.96 0.89-1.03 0.203

Hemoglobin at ED 1.10 0.86-1.42 0.453

pH at ED 0.00 0.00-1118.56 0.492

Delta neutrophil index at ED 0.99 0.71-1.39 0.970

CRP 1.11 0.86-1.43 0.431

White blood cell count at ER (per dL) 1.00 1.00-1.00 0.498

Neutrophil (%) at ED 1.00 0.96-1.05 0.901

Amylase (U/L) at ED 0.98 0.96-1.00 0.063

Lipase (U/L) at ED 1.00 1.00-1.00 0.084

Lactate (mmol/L) at ED 1.22 0.78-1.93 0.384

COPD, chronic obstructive pulmonary disease; ED, emergency department; HU, Hounsfield unit; CT, computed tomography; GCS, Glasgow comma scale; CRP, C-reactive protein

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Supplement table 5. Comparison of HU between No Hollow Viscus Perforation and Hollow Viscus Perforation groups

No Hollow Viscus Perforation

(n = 42)

Hollow Viscus Perforation (n = 14) P-value*

Hounsfield units 37.9 ± 14.9 21.6 ± 15.6 0.001

*Student’s t-test

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